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The first method for private media transmission includes wire lines or buried cable and modems, and is usually limited to low bandwidth. When it makes sense for a company to string or bury its own communication cable between sites, companies should consider staffing requirements necessary to support technical/maintenance aspects of system.
The second method to consider is wireless transmission and includes spread spectrum, microwave or VHF/UHF radios.
Spread Spectrum is license-free and available to public in 900 MHz and 5.8 GHz bands. Some spread spectrum radios have ability to re-strengthen signals for next radio in line. These repeater radios are used to span distances and generally have built-in error correction, encryption and other features, making them a reliable, secure and long-lasting solution for network communication.
Microwave radio transmits at high frequencies through parabolic dishes mounted on towers or on top of buildings. This media uses point-to-point, line-of-sight technology and communication may become interrupted at times due to misalignment and/or atmospheric conditions.
VHF/UHF radio (good for up to 30 miles) is an electromagnetic transmission with frequencies of 175 MHz-450 MGz-900 MHz received by special antennas. A license from FCC must be obtained and coverage is limited to special geographical boundaries.
Public media transmission includes services offered by a local telephone or cable company, and in some systems and/or subsystems, it may provide a more suitable method for data transfer. The Public Switch Telephone Network, Generally Switched Telephone network, and Cellular network are dial-up services suitable for occasional use. If a 24-hour permanent connection for analog data transmission between two or more locations is needed, Private Leased Line should be considered. The Digital Data Service with DSL and ISDN, systems recently popularized by broadband/cable Internet, should be considered for high speed/low error rate, computer-to-computer applications. WiFi equipment utilizes broadband as well, but on a time-share basis when it makes sense to use infrastructure of another company. PCS/CDPD service, provided by cellular companies and Low Earth Orbit or geosynchronous satellites can also be used for continuous communication.
Finally, employment of an easy-to-use SCADA software package, commonly know as human machine interface (HMI), installed on PC hardware provides a reliable representation of real system at work. An HMI allows operator to view virtually all system alerts, warnings and functions as well as change set points and analyze, archive or present data trends.
Some common HMI software packages include Cimplicity (GE-Fanuc), RSView (Rockwell Automation), IFIX (Intellution) and InTouch (Wonderware). Most of these software packages use standard data manipulation/presentation tools for reporting and archiving and integrate well with Microsoft Excel, Access and Word. Collected data can also be sent to Web servers that dynamically generate HTML pages to be viewed on operator’s LAN or published to Internet.
The Microprocessor Option With this basic understanding of SCADA system components, a facility may want to consider utilizing a microprocessor and/or PLC-based SCADA system over a basic RTU or a proprietary system for following reasons:
Microprocessors (MPs), like MTUs, can continuously collect, process and store data, operating independently from MTU through “intelligent” programming. In addition, by utilizing a microprocessor-based level meter, a SCADA system provides both a master and local display that automatically gathers, processes and reports data necessary to comply with local, state and federal regulations in formats that integrate well will Microsoft Excel, Access and Word.
Microprocessors can provide security and monitoring of door switches, heat and motion detectors. Managers/operators can be informed 24 hours a day through automatic e-mail, paging and dial-up call features. Multiple users can easily be added and, if open architecture protocol is used, future equipment can easily be integrated. Since MPs have no moving parts, they are extremely reliable and can be designed to be repairable with components that any local electrical distributor supplies.
Microprocessor-based SCADA systems can reduce number of man-hours needed for on-site visual inspections, adjustments, data collection and logging. Continually monitoring and troubleshooting potential problems increases equipment life, reduces service calls, reduces customer complaints and increases system efficiency. Simply put, open-architecture, microprocessor-based SCADA systems are an excellent means for process control facilities to save time and money.
Review The return on investment and benefits produced by a properly engineered microprocessor-based SCADA system far outweigh initial investment if right equipment is chosen and installed correctly. But from hundreds of SCADA system providers to choose from, one poor decision may lead down path to countless frustrations, inefficiencies and unnecessary expenses.
Hopefully, by conducting a pre-SCADA system assessment, facilities will be better equipped to avoid such problems . . .
This is an edited version of company’s Pre-SCADA Assessment white paper. For a full copy, visit www.epgco.com/scada-assessment.html or contact Randy Dennison at 800-443-7426
Randy Dennison is Marketing Manager for NBT, EPG Companies Inc. SCADA and telemetry division. NBT manufacturers SCADA and Telemetry equipment for the Water and Wastewater Industry as well as for landfills and remediation sites. For more information, call 800-443-7426 or go to www.nbtinc.com or www.epgco.com